Pronephrium Subg. Pronephrium Sect. Dimorphopteris (Tagawa & K. Iwats.) Holttum
Content
Description
Plants of moderate size, always with a relatively short deltoid apical lamina on fronds of adult plants, young plants rarely (as in P. meniseiiearpon) having simple fronds 10 cm or more long;
Distribution
Asia-Tropical: India present, Ceylon present, Pacific: Fiji (Fiji present), Palau island present, S. China present
45 species, all Malesian (P. beccarianum extending to Fiji) except P. articulatum (Houlst. & Moore) Holttum in Ceylon, India to S. China, and P. palauense (Hosokawa) Holttum in Palau island.
Notes
I suggest that a probable prototype for this section is shown by the Indian species P. articulatum (see Holttum 1972: 116); the Malesian P. glandulosum differs from it in smaller size and greater abundance of glands. The other species are mostly still smaller, with a pronounced tendency to dimorphism, the most extremely dimorphic being the type species P. moniliforme.
This section agrees with Sphaerostephanos in the presence of spherical yellow glands, on either the lower surface of pinnae or on indusia or sporangia, in a majority of species; it differs from Sphaerostephanos in the absence of much-reduced basal pinnae and (in most species) in the pustular nature of the lower surface of dried fronds. But there appears to be an evolutionary trend within Sphaerostephanos towards reduction in the number of such small basal pinnae, and there are species in which some fronds may have 1-2 pairs of reduced pinnae and others none, on the same plant. I see no sharp distinction between such species and others which have no reduced basal pinnae. Thus on this character there appears to be no clear Separation of this section from Sphaerostephanos. The section does however give the impression of being natural if one excludes from it species with deeply lobed non-pustular normal pinnae (e.g. Nephrodium diversilobum Presl); such species are here placed in Sphaerostephanos (in some cases they have obvious relatives in that genus). Even when this is done, the present section may still include species of two different ancestral origins: those derived from ancestors with, and without, reduced basal pinnae. The whole problem of recognizing affinities is complex; the present arrangement is one of convenience pending further investigation of an experimental nature.
The present arrangement includes some species placed in sect. Pronephrium in 1972; P. buwaldae Holttum, included here in 1972, is now transferred to Christella.
This section agrees with Sphaerostephanos in the presence of spherical yellow glands, on either the lower surface of pinnae or on indusia or sporangia, in a majority of species; it differs from Sphaerostephanos in the absence of much-reduced basal pinnae and (in most species) in the pustular nature of the lower surface of dried fronds. But there appears to be an evolutionary trend within Sphaerostephanos towards reduction in the number of such small basal pinnae, and there are species in which some fronds may have 1-2 pairs of reduced pinnae and others none, on the same plant. I see no sharp distinction between such species and others which have no reduced basal pinnae. Thus on this character there appears to be no clear Separation of this section from Sphaerostephanos. The section does however give the impression of being natural if one excludes from it species with deeply lobed non-pustular normal pinnae (e.g. Nephrodium diversilobum Presl); such species are here placed in Sphaerostephanos (in some cases they have obvious relatives in that genus). Even when this is done, the present section may still include species of two different ancestral origins: those derived from ancestors with, and without, reduced basal pinnae. The whole problem of recognizing affinities is complex; the present arrangement is one of convenience pending further investigation of an experimental nature.
The present arrangement includes some species placed in sect. Pronephrium in 1972; P. buwaldae Holttum, included here in 1972, is now transferred to Christella.